1. Field of the Invention
The present invention relates to a method of renewing a track comprised of two used rails fastened to used ties in an operating direction, which comprises the steps of continuously lifting the used rails off the used ties, continuously and sequentially replacing the used ties by new ties at a tie replacement track section progressing continuously in the operating direction, and continuously welding adjoining ends of new rail sections together to form endless welded rails and laying the endless welded rails on the new ties, and to a machine arrangement for carrying out this method, which comprises a plurality of mobile machine units each comprising machine frame means respectively carrying devices for lifting the used rails off the used ties and continuously and sequentially replacing the used ties by new ties and laying the endless welded rails on the new ties, and a device for welding adjoining ends of new rail sections together to form the new endless rails.
2. Description of the Prior Art
Patent application no. PCT/EP90/00819, published Nov. 29, 1990, under No. WO 90/14470 discloses a continuous track renewal wherein new rail sections to be laid on new ties are welded together immediately before they are laid. The welding station precedes the tie replacement in the operating direction of the track renewal, the endless welded rails being guided over the gap between the old and new tracks to be laid on the new ties. This has the disadvantage that the distance between the welding station and the rail laying station is quite large so that the artificially produced rail laying temperature can be maintained only by producing an excessively high temperature. This system requires a uniform rail laying speed which may be difficult to achieve because the tie and rail laying must be coordinated, and the tie replacing operation may encounter difficulties.
German Pat. No. 3,229,878, published Mar. 3, 1983, deals with the welding of adjoining ends of rail sections to form endless welded rails. This rail welding machine comprises a machine unit comprised of a series of successive machine frames and a rail transport car preceding the machine unit in the operating direction. The rail transport car is succeeded by a machine frame for raising the rail sections to the level of a welding head designed to weld adjoining ends of the rail sections together, and the welding head is transversely displaceable to enable it to weld both rails of the track. The endless welded rails are then pulled by a device following the welding head, and the endless welded rails are temporarily laid on the track behind the machine unit, for example centrally between the old rails, until the track is renewed by a succeeding track renewal train. This machine arrangement has the disadvantage that the endless welded rails must be temporarily stored on the old track, which makes cleaning of the ballast before the new track is laid impossible. Furthermore, the rails must be spread apart in the track renewal track to make the tie exchange possible and must then be moved together for laying at the desired track gauge.
U.S. Pat. No. 3,633,513, dated Jan. 11, 1972, discloses a work train for the continuous replacement of an old track by a new track, which comprises a plurality of independently movable machine frames respectively carrying tie and rail replacement devices.
U.S. Pat. No. 3,896,734, dated Jul. 29, 1975, discloses a similar track renewal train. This train includes a butt-welding head on one of the machine frames for butt-welding rail sections, temperature conditioning apparatus on succeeding machine frames for regulating the temperature of the continuous welded rails, and succeeding machine frames spaced a distance from the welding station for laying the temperature-conditioned continuous welded rails on the ties. This machine arrangement has the disadvantages described hereinabove in connection with WO 90/14470.